These are tense times for scientists and engineers at NASA's Jet Propulsion Lab in Pasadena. Late Sunday night Pacific Time, they'll learn if nearly a decade of hard work will result in a priceless scientific laboratory landing safely on Mars or if the rover known as Curiosity will turn into a useless pile of junk. Everything depends on what happens during the seven minutes of terror, the time it takes the probe to go from the top of the Martian atmosphere to the planet's surface.

NPR science correspondent Joe Palca has been covering the mission. He has these thoughts about this time of anxious waiting.

JOE PALCA, BYLINE: I feel a certain connection with this mission. I've made it a point to check in on Curiosity over the past few years. In 2010, principle mission scientist John Grotzinger took me to a balcony overlooking an enormous clean room at the Jet Propulsion Lab, where technicians in white suits fussed over gleaming pieces of hardware.

This is the real deal, right? This is the thing that's going to be on Mars in a couple of years.

JOHN GROTZINGER: Right. So what we see in the high bay viewing gallery here are all the components that are going to come together to form the spacecraft that will eventually land on the surface of Mars.

PALCA: Eventually seem a long way off back then. Now, eventually as arrived. Everything has to work perfectly during those seven minutes of terror for Curiosity to land safely. Adam Stelzner is the engineer in charge of the team that built the landing system. At a news conference, a reporter asked him whether there was any one of those seven minutes he was particularly concerned about.

ADAM STELZNER, JET PROPULSION LABORATORY: Like any good parent, I love each of those minutes equally.

(LAUGHTER)

LABORATORY: In different ways, of course. They're all different minutes.

PALCA: Stelzner uses humor to cope with the crushing anxiety and he does a pretty good job, but really, they'll be no relief until 10:31 Pacific Time on Sunday night. That's when Curiosity is due to send its first signal from the Martian surface. David Blake of NASA's Ames Research Center is in charge of one of Curiosity's instruments. He tries to take a philosophical approach to the whole thing.

DAVID BLAKE NASA: The crazy thing about this whole business is there's nothing about this that's a done deal, you know. It's like running in the Olympic Games. You just don't know if you're going to get the medal. You do everything you can and hope for the best.